Methods for cutting sharp corners and notches in layups of fabric and other sheet material

ABSTRACT

A layup of sheet material is cut by a cutter having a reciprocating cutting blade with a sharp forward cutting edge. During cutting along a given line of cut the cutting blade extends through the layup during at least a portion of each of its strokes, and when a sharp corner or notch point is reached the blade is rotated while remaining in cutting engagement with the layup to turn the corner or to cut the notch without the blade being first withdrawn from the material or without being moved through a path departing from the desired line of cut.

[111 3,766,813 Oct. 23, 1973 United States Patent [1 1 Pearl Lefkowitz et al.

[ METHODS FOR CUTTING SHARP 1,923,834 8/1933 CORNERS AND NQTCHES [N LAYUPS 3,573,859 4/1971 Sederberg........... FABRIC AND OTHER SHEET MATERIAL 3,587,381 6/1971 Sederberg.............

[75] Inventor: David Raymond Pearl, West Hartford, Conn.

Primary ExaminerJ. M. Meister Att0rneyRoger B. McCormick et al.

T C A R T S B A .H a n I v. g h 0 n .m. n e

H o MC m r 7. mm m 6H mm a GE m e n w 8 S A M 7 [22] Filed:

Aug. 5, 1971 A layup of sheet material 18 cut by a cutter having a No.: 169,264

[21] App].

reciprocating cutting blade with a sharp forward cutting edge. During cutting along a given line of cut the cutting blade extends through the layup during at least a portion of each of its strokes, and when a sharp corner or notch point is reached the blade is rotated while remaining in cutting engagement with the layup to turn the corner or to cut the notch without the blade being first withdrawn from. the material or with- 7 2 CH6N 9 l5 3 3 896 7 2 2 13B5 a 6 2 5 H 3 .l 8 W40 dB 6 5 6 7 2 .1 a B m m mmC m mm WW5 n 2 m m mh R n r. U 84 e i m 7 L $12 C '04 N 5 MR U IF 1111 2 8 5 .l.

out being moved through a path departing from the desired line of cut.

[56] References Cited UNITED, STATES PATENTS 3,245,295 4/1966 Mueller................................... 83/56 6 Claims, 22 Drawing Figures PATENTEDUBT23 ms 3.766.813

sum 1 OF 3 I'NVENTOR. DAVID R. PEARL A TTOR/VE Y5 METHODS FOR CUTTING SHARP CORNERS AND NOTCHES IN LAYUPS OF FABRIC AND OTHER SHEET MATERIAL BACKGROUND OF THE INVENTION This invention relates to methods for use in cutting layups of sheet material by means of a cutter having a reciprocating cutter blade, and deals more particularly with such methods involving the cutting of layups along a desired line of cut including two line segments which meet at a relatively sharp corner which sharp corner may be a corner formed by two segments of the principal line of cut or a corner defined by the intersection of the principal line of cut with a marking notch.

In the cutting of fabrics and other sheet material to produce pieces for garments, upholstery and the like it is well known to lay up a number of layers of sheet ma terial on a cutting table and to then cut all of the layers simultaneously by means of a cutter having a reciprocating cutting blade which during cutting extends entirely through the layup during at least a portion of each of its reciprocating strokes. The pieces cut from the layup are defined by principal lines of cut which quite often include one or more relatively sharp corners. The cutting blade has a sharp forward cutting edge and usually has a substantial front to rear dimension. Because of this substantial front to rear blade dimension it has been customary in the past when reaching a sharp corner to move the blade along a subsidiary path, departing from the line of cut and passing through a waste region of the layup or through a free area beyond the bounds of the layup, throughout which subsidiary path the blade is turned so that when it again approaches the corner it is aligned with the line of cut on the departing side of the corner. This not only requires the existence of some waste or free area adjacent each corner to allow for the maneuvering of the blade, but also is a time-consuming procedure. As an alternative, in cases where the cutting blade is of the cantilever type when reaching a corner the blade may be withdrawn from the material, rotated outside of the material, and then plunged back into the material at the corner point with the blade now oriented to follow the line of cut away from the corner. This eliminates the need for providing a waste or free areaadjacent the corner but is still a time-consuming procedure.

In the cutting of pattern pieces from layups of sheet material, it is also often desired to produce marking or index notches, at various points along the principal de sired line of out, these marking notches being later used, for example, to align various different pattern pieces relative to one another in preparation for a sewing operation or the like. Generally the marking notches are relatively short lines or slits which are cut into the material generally perpendicularly to the principal line of cut. The problems involved in cutting these notches are substantially the same as those involved in cutting sharp corners, and in the past notches have usually been cut by maneuvering the cutting blade, outside of the pattern piece, to bring it into proper orientation for cutting a notch before it is moved inwardly of the piece beyond the principal line of cut to produce the notch. This may be done by either cutting the notch immediately upon reaching the notch point or by cutting along the principal line of out past the notch point and later returning to cut the notch. Both procedures, however, involve a substantial amount of maneuvering of the blade and a substantial consumption of time. Furthermore, where two pattern pieces share a common boundary line it is usually impossible to cut a marking notch into either of such pieces without first entirely cutting at least one of the pieces from the layup and shifting it relative to the other piece so as to provide freespace for manuevei'ing the blade.

The general object of this invention, therefore, is to provide improved methods of cutting sharp corners and notches in layups of fabric and other sheet material whereby the necessity of allowing waste or free areas near sharp corners and common boundary lines is elim inated thereby allowing the pattern pieces to be laid out closer to one another with a resulting economy of material. A related object is to provide such methods whereby the time required for cutting sharp corners and notches is minimized. A more specific object of the invention is to provide a method for cutting notches substantially on the fly as the cutting blade is moved along a principal line of cut by merely momentarily rotating or flicking the blade away from the line of cut to swing its cutting edge into the pattern piece.

SUMMARY OF THE INVENTION This invention resides in a method for cutting a sharp corner or a notch in a layup of sheet material by means of a cutter having a reciprocating cutting blade with a sharp forward edge and a rear edge spaced a substantial distance rearwardly from the sharp edge. During the cuttingof the layup along a desired line of cut the blade is maintained at a fundamental crutting height relative to the layup, whereat it extends entirely through the layup during at least a portion of each stroke, and it is reciprocated and moved forwardly along the line. When a corner or notch point is reached the reciprocation of the blade is continued and the blade is maintained at its fundamental cutting height. The blade is further rotated about an axis parallel to the cutting edge in such a direction as to move the cutting edge away from the corner or notch point along the desired line of cut departing from such corner or notch point.

In the case where the line departing from the corner or notch point is a straight line the blade is also advanced relative to the layup to cause the cutting edge of the blade to follow the desired straight line. In the case of cutting a notch the cutting edge of the blade is returned to the notch point after the notch line is cut and the blade is then again advanced forwardly away from the notch point along the principal line of cut. Preferably, when cutting a notch the rotational axis of the blade is held stationary relative to the layup as it is rotated so that the cutting edge cuts the material along a curved notch line.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary perspective view of a sheet material cutting apparatus with which the method of this invention may be used.

FIG. 2 is an enlarged fragmentary vertical sectional view taken through the layup of FIG. 1 in the vicinity of the cutting blade.

FIG. 3 is a fragmentary top view of a portion of the layup of FIG. 1 showing a number of pattern pieces to be cut therefrom.

FIGS. 4A to 4E are views showing progressively themovement of the blade of FIG. 1 as it cuts a notch in accordance with one embodiment of this invention.

FIGS. 5A to 5H are a series of views showing progressively the movement of the blade of the apparatus of FIG. 1 as it cuts a notch in accordance with another embodiment of this invention.

FIGS. 6A to 6B are a series of views which progressively show the movement of the blade of FIG. 1 as it cuts a corner in accordance with one embodiment of this invention.

FIG. 7 is a view showing the position of the blade of the apparatus of FIG. 1 at one point in its movement at it cuts a corner in accordance with still another embodiment of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 a sheet material cutting apparatus of the type with which this invention may be used is indicated generally at 10 and consists of a table 12 providing support for a layup 14 comprising a plurality of sheets of fabric or other material arranged in vertically stacked relation. A carriage indicated generally at 16 is supported by the table for traversing the surface thereof in two coordinate directions as indicated by the arrows X and Y. A cutter 17 having a cutting tool in the form of a blade 18 is mounted on the carriage 16 so that it can be driven to and from any predetermined point relative to the table surface in response to position signals supplied to the apparatus through the cable 19 from an associated source such as, for example, a numerically controlled controller or computer 20. The carriage 16 is capable of moving the blade 18 in cutting engagement with the layup 14 along any desired line which may be either straight or curved as required in cutting a garment or upholstery component or the like. The blade 18 has a reciprocating cutting stroke and is capable of being rotated, by positioning signals from the controller 20, about a vertical axis, perpendicular to the generally horizontal layup 14, as indicated by the arrow 0.

The blade 18 may be moved from a fundamental cutting height to a fundamental withdrawn height relative to the layup 14. At the cutting height the blade during at least a portion of each stroke penetrates entirely through the material so that all the layers of the material are cut as the blade is advanced forwardly along a given line of cut. At its withdrawn height, the blade throughout its entire stroke is located above the material so that it may be moved to any point on the layup without cutting the layup during such movement. FIG. 2 shows the blade 18 in its fundamental cutting position, the solid lines showing it at the bottom of its stroke and the broken lines showing it at the top of its stroke. As shown in FIG. 2, the blade has a sharp forward cutting edge 22 extending vertically parallel to the axis of reciprocation, and also has an unsharpened rear edge 22 located a substantial distance rearwardly from the sharp edge 20.

The supporting surface 24 of the table 12 is made of a bed of penetrable material and the blade 18 during its reciprocation extends downardly beyond the lower layer of the layup so as to penetrate the supporting surface. The material of the layup is also preferably held in place during the cutting operation by a vacuum holddown means consisting of a sheet 28 of airimpermeable material overlying the layup and having a vacuum applied to its undersurface so that atmospheric pressure presses it and the layup toward the supporting surface. This vacuum may be applied from a vacuum chamber 30 located below the bed 26 and communicating with the layup 14 through a large number of openings, 32, 32 passing through the bed. US. Pat. No. 3,495,492 entitled Apparatus for Working on Sheet Material" shows a suitable vacuum holddown system which may be used with the apparatus of FIG. 1, and reference may be had to said patent for further details. A presser foot 31 attached to the cutter 17 may also be used in conjunction with the vacuum holddown to aid in holding the material of the layup 14 in place in the vicinity of the cutting zone.

The carriage 16 is carried by a larger main carriage indicated generally at 34 which transversely spans the table 12 and is supported at both ends by a pair of elongated racks 36, 36 on opposite sides of the table. A drive motor 38 through suitable drive mechanism drives the carriage 16 relative to the carriage 34 in the illustrated X-direction and another drive motor 48 through suitable drive mechanism drives the main carriage 34 in the Y-direction along the racks 36, 36. Another drive motor in the cutter 17 rotates the blade about the 6 axis.

Referring now to FIG. 3, this figure shows an exemplary layout of pattern pieces to be cut from a layup of sheet material such as that shown at 14 in FIG. 1. Several different pattern pieces are indicated by the reference numerals 42, 44 and 46. Each of these pattern pieces is defined by a principal boundary line 48 which may include one or more sharp corners sch as indicated for example at 50, 50. Also, along each principal line 48 may be one or more notches 52, 52 which extend inwardly a short distance from the boundary line so as to constitute essentially shallow slits in the edge of each pattern piece which may be used to later match the pattern piece with another one in making up a garment. It will be noted in FIG. 3 that the illustrated pieces 42 and 44 along parts of their lengths share a common boundary and that similarly the pieces 44 and 46 along parts of their lengths also share a common boundary. Along these common boundaries it is therefore necessary when cutting notches or sharp corners to make certain that the cutting blade does not depart from the principle line or from the notch line so as to cut an undesired line in one or the other of the neighboring pattern pieces. The methods hereinafter described for maneuvering the blade during the cutting of the pattern pieces avoids this problem and allow the sharing of common boundary lines as indicated in FIG. 3.

In accordance with this invention the cutting blade 18 is maintained within the layup, is reciprocated, and is rotated, or rotated and advanced, when it reaches a corner or notch point so as to cuase the cutting edge of the blade to immediately follow the line departing from the comer or notch point without the blade having to first execute a turning maneuver through waste material or free space. FIGS. 4A and 4E, for example, show the manner in which the blade 18 is moved in cutting a notch 52 in accordance with one embodiment of this invention. In these figures the broken line 48 represents the principal line to be followed by the blade 18 and the solid line 48 represents that portion of such line already cut. Likewise, the broken line 52 represents the notch line to be cut and the solid line 52 represents such line after it is cut. The reference numeral 54 indicates the notch point at which the notch line 52 intersects the principal line 48. FIG. 4A shows the blade 18 as it approaches the notch point 54. At this time, the blade 18 is at its fundamental cutting height, it is being reciprocated and it is being moved forwardly toward the notch point 54 in the direction of the arrow 56. This activity is continued until the forward edge of the blade 18 reaches the notch point 54 as shown in FIG. 4B. When the position of FIG. 4B is reached the movement of the blade in the plane of the layup is discontinued and then, while the blade remains at its fundamental cutting height and while its reciprocation is continued, the blade is rotated about a vertical axis to swing its cutting edge 20 away from the principal line of cut 48 and to cause it to cut along the notch line 52. FIG. 4C shows the blade 18 in the maximum extent of its rotation away from the principal line 48. This rotation of the blade is accompanied by a displacement of the material on the side of the blade toward which the blade is rotated and is indicated by the wrinkles 58 in FIG. 4C.

After the notch line 52 has been cut by rotating the blade to the FIG. 4C position, the blade is rotated in the reverse direction to bring its cutting edge 20 back to the principal line 48 and notch point 54, as shown in FIG. 4D. Thereafter, the blade is again moved forwardly along the principal line 48 and away from the notch point 54 as shown in FIG. 4E.

Throughout all of the movements represented by FIGS. 4A to 4E, the blade is maintained at its fundamental cutting height and is reciprocated, and it will be noted that the cutting edge 20 at no time departs from the lines desired to be cut. The method of notch cutting shown by these figures is one which allows for the cut ting of the notches essentially on the fly" since when a notch point is reached the notch may be cut very quickly by only momentarily stopping the forward ad vance of the blade along the principal line of cut and rotating it quickly back and forth in a fast flicking mo tion to execute the notch. In FIGS. 4A to 4E the blade 18 during its rotation is shown to be rotated about a rotational axis generally coincident with the rear edge 22. This is preferred in that it allows a maximum depth notch with minimum radius of curvature. This is not essential, however, and if desired, the blade may be rotated about some other rotational axis located to the rear of the cutting edge.

In the notch cutting method of FIGS. 4A to 4E the blade is not advanced relative to the material as it is rotated, and as a consequence the notch 52 is of a curved shape as illustrated. This curved shape is usually acceptable, but in some instances it may be desired to have the notches cut along straight lines. Wen this is so the blade, in practicing the method of this invention, must be advanced as well as rotated while cutting a notch. FIGS. 5A to 5H show the cutting of a straight notch in accordance with another embodiment of this invention. In these figures the same reference numerals are used as in FIGS. 4A to 4E except that the notch is shown at 60, in broken line form before cutting and in solid line form after cutting.

Referring to FIGS. 5A to 5H, FIG. 5A shows the blade 18 as it approaches the notch point 54. At this time the blade is at its fundamental cutting height and is reciprocated and is moved forwardly toward the notch point 54 as indicated by the arrow 56. This activity is maintained until the cutting edge 20 of the blade reaches the notch point 54, as shown in FIG. 5B. As the FIG. 58 position is reached the blade is maintained at it fundamental cutting height in the material and is continued to be reciprocated, and this maintenance of the cutting height and continuance of the reciprocation prevails throughout all of the other stages of the notch cutting procedure up to and beyond the stage represented by FIG. 5H. At the point shown by FIG. 58, however, the normal forward travel along the principal line 48 is stopped and the blade is moved away from the I line 48 to cut the notch 60. Since the line of the notch is straight rather than curved the notch cannot be cut merely by rotating the blade. Instead the blade is both rotated about a rotational axis parallel to the cutting edge and the rotational axis is moved in the plane of the layup to cause the cutting edge to follow the desired straight line.

In FIGS. 5A and 5H the rotational axis of the blade I8 is taken to be generally coincident with the rear edge 22 thereof. FIG. 5C shows the blade 18 at a point representing a slight rotation away from the position of FIG. 5B. Also, by comparing FIG. 58 with FIG. 5C it will be noted that the rear edge of the blade 22 has been moved relative to the layup 114 to a position closer to the notch point 54. FIG. 5D shows the blade 18 at a subsequent point whereat it has been rotated a still further distance away from the principal line 48 and whereat the rear edge of the blade 22 has been moved still closer to the notch point 54.

FIG. 5C shows a later position of the blade 18 at which it has been rotated to the point at which its rear edge 22 is in line with the notch line 60 and moved alongthe notch line 60 to cut the notch to it full depth.

After the blade is moved to the full depth notch position of FIG. 5E it is then returned in a reverse manner to bring the cutting edge back to the notch point and the blade is then again advanced along the principal line 48 in the normal manner. FIG. 5F shows the blade 18 returned partway to the notch point 54 and FIG. 50 shows it fully returned. FIG. 5H shows it after being advanced in the direction of the arrow 56 beyond the notch point 54, and this advancing movement is continued until the next notch point or corner is reached.

One advantage of the methof of notch cutting shown by FIGS. 5A to 5H is that it allows for the cutting of any depth notch. That is, the length of the notch may be less than, equal to or greater than. the front to rear dimension of the blade. In the illustrated case the notch 60 has been shown to be made slightly longer than the blade, but it obviously could be made longer, and it could also be made shorter by stopping the illustrated notch cutting procedure at any point and returning the blade to the notch point. Also, it will be understood that the amount by which the rotational axis is advanced in response to a given increment of rotation in order to keep the cutting edge of the blade on the desired line is a matter which may be easily calculated and stored in the controller or computer 20 as part of a notch cutting routine.

The general method for notch cutting illustrated by FIGS. 5A and 5H may also be used in part for cutting sharp corners, if desired. That is, the cutting of the notch 60 is basically a corner cutting operation except that after the corner is turned the blade is reversed to bring it back to the notch point and is then continued on along the principal line of cut. Considering the line 60 of FIG. 5A to be a line defining a corner with the line 48, the movement of the blade 18 to cut the corner would involve the steps shown by FIGS. 5A to SE with the blade continuing forwardly along the line 60 after reaching the point of FIG. E.

In FIGS. 4A to 4B and FIGS. 5A to SE the blade when rotated is rotated about a rotational axis generally coincident with its rear edge so that the rear edge remains on the principal line of cut 48 during the rotation process. This in turn means that practically all of the displacment of the material of the layup which occurs to accommodate the rotation of the blade occurs in that material which lies adjacent the side of the blade towards which the blade is turned. That is, the side of the blade towards which it is turned pushes away the material and the opposite side of the blade is substantially free of engagement with the material. In some cases it may be desirable to reduce the amount of material displacement required and this may be accomplished by rotating the blade about an axis located between its cutting edge and its rear edge. Such a manner of rotation is shown in FIGS. 6A to 6E from which it will be noted that the displacement of the material occurs on both sides of the blade.

Referring to FIGS. 6A and 6E, these figures show the blade as moved to cut a sharp corner. The corner point is indicated at 62 and is defined by two segments 48a and 48b of the principal line. Throughout all of the stages illustrated the blade 18 is maintained at its fundamental cutting height and is continuously reciprocated. FIG. 6A shows the blade 18 advancing toward the corner point 62 at which time it is moving generally in the direction of the arrow 56. This activity is maintained until the corner point 62 is reached by the cutting edge 20 of the blade as shown in FIG. 6B. Thereafter, the cutting blade 18 is rotated about an axis 64 located between the cutting edge 20 and rear edge 22 to cause the cutting edge 20 to swing away from the corner point 62 along the line segment 48B and to also cause the rear edge 22 of the blade to swing outwardly away from the previously cut line segment 48A. Therefore, both side edges of the blade push against the material of the layup and displace it to accommodate the turning movement of the blade.

Following the point shown by FIG. 6C the blade 18 is further rotated about its rotational axis and the rotational axis is moved relative to the layup 14 to move the cutting edge 20 further forwardly along the line segment 48b to the point shwon at FIG. 6D, and then to the point shown at FIG. 6E whereat the blade 18 has both its cutting edge 20 and its rear edge 22 aligned with the line segment 48b and is traveling away from the corner point 62. From FIG. 6D it will be noted that the rotational axis 62 does not necessarily remain on the line segments 48a and 48b and the exact course which such rotational axis follows as the blade rotates may be predetermined and stored in the controller 20 as part of the corner cutting routine. It will also, of course, be understood that the corner cutting method of FIGS. 6A to 6D may also be used as part of a notch cutting method, the notch cutting method merely requiring that the blade 18 be returned from the position of FIG. 6E to the line segment 48a and then advanced again forwardly along the line segment 48a assuming that the segment 48a extends further to the left than shown in these figures.

In all of the notch and corner cutting methods discussed above the blade 18 has been driven with its cutting edge and its rear edge in line with the desired line of cut until the notch point or corner point is reached, and no rotation of the blade occurs until this time. In some cases, however, it may be desirable to initiate rotation of the blade slightly in advance of reaching the notch point or corner point, the cutting edge, however, remaining on the desired line of cut. FIG. 7, for example, shows this condition. In this figure, the blade 18 is approaching the corner point 62 and as it nears said point its rear edge is swung away from the line segment 48a to head its cutting edge 20 slightly toward the line segment 48b, but the rotational axis of the blade is also moved away from the line 480 so as to maintain the cutting edge on the line 48a. It will, of course, be understood that after the corner point is reached by the cutting edge 20 the blade 18 is further rotated and translated in the plane of the layup to cause the edge 20 to move away from the corner point and follow along the line segment 48b.

I claim:

1. A method for use in cutting a layup of sheet material by means of a cutter having a cutting blade reciprocated along an axis generally perpendicular to the layup being cut and having a forward cutting edge and a rear edge both extending generally parallel to said axis of recirporocation, said method involving the cut-' ting of the layup along a principal line of cut and along a notch line located at a given notch point along said principal line and extending to one side thereof at a relatively sharp angle thereto, said method comprising the steps of advancing said cutting blade, with its cutting edge directed forwardly along said principal line while reciprocating it and maintaining it at a fundamental cutting height relative to said layup wherein it extends entirely through said layup during at least a portion of each stroke, when said notch point is reached rotating said blade, while continuing its reciprocation and while maintaining it at said fundamental cutting height, in such a direction as to move said cutting edge away from said notch point along said notch line, thereafter rotating said blade in the opposite direction to bring said cutting edge back to said notch point, and then again advancing said blade forwardly along said principal line away from said notch point.

2. A method as defined in claim 1 further characterized by maintaining said rear edge of said blade on said principal line during said rotation of said blade.

3. A method as defined in claim 1 further characterized by said step of rotating said blade being accomplished by rotating it about an axis located rearwardly of said cutting edge.

4. A method as defined in claim 3 further characterized by holding said axis of blade rotation stationary relative to said principal line during said rotation of said blade.

5. A method as defined in claim 4 further characterized by said axis of rotation being generally coincident with said rear edge of said'blade.

6. A method as defined in claim 1 further characterized by moving said axis of rotation relative to said layup during the rotation of said blade to cause said cutting edge to follow a substantially straight notch line. 

1. A method for use in cutting a layup of sheet material by means of a cutter having a cutting blade reciprocated along an axis generally perpendicular to the layup being cut and having a forward cutting edge and a rear edge both extending generally parallel to said axis of reciprocation, said method involving the cutting of the layup along a principal line of cut and along a notch line located at a given notch point along said principal line and extending to one side thereof at a relatively sharp angle thereto, said method comprising the steps of advancing said cutting blade, with its cutting edge directed forwardly, forwardly along said principal line while reciprocating it and maintaining it at a fundamental cutting height relative to said layup wherein it extends entirely through said layup during at least a portion of each stroke, when said notch point is reached rotating said blade, while continuing its reciprocation and while maintaining it at said fundamental cutting height, in such a direction as to move said cutting edge away from said notch point along said notch line, thereafter rotating said blade in the opposite direction to bring said cutting edge back to said notch point, and then again advancing said blade forwardly along said principal line away from said notch point.
 2. A method as defined in claim 1 further charaCterized by maintaining said rear edge of said blade on said principal line during said rotation of said blade.
 3. A method as defined in claim 1 further characterized by said step of rotating said blade being accomplished by rotating it about an axis located rearwardly of said cutting edge.
 4. A method as defined in claim 3 further characterized by holding said axis of blade rotation stationary relative to said principal line during said rotation of said blade.
 5. A method as defined in claim 4 further characterized by said axis of rotation being generally coincident with said rear edge of said blade.
 6. A method as defined in claim 1 further characterized by moving said axis of rotation relative to said layup during the rotation of said blade to cause said cutting edge to follow a substantially straight notch line. 